Method for removal of copper from lead



METHOD FOR REMOVAL OF COPPER FROM LEAD Original Filed Aug. 31. 1966 2 Sheets-Sheet 1 INVENTOR Wladz mz'r W K'rysko ATTORNEYS July 9, 1968 w. w. KRYSKO 3,392,011

METHOD FOR REMOVAL OF COPPER FROM LEAD Wladmr W ifrysko BY $4M? M ATTORNEYS United States Patent 3,392,011 METHOD FOR REMOVAL OF CGPPER FROM LEAD Wladimir W. Krysko, Sydney, New South Wales, Australia, assignor to Metallgesellschaft Aktiengesellschaft, Frankfurt am Main, Germany Continuation of application Ser. No. 576,344, Aug. 31, 1966. This application May 29, 1967, Ser. No. 642,242 Claims priority, application Australia, Aug. 12, 1963, 34,082/63; Germany, Apr. 1, 1965, M 64,734 1 Claim. (Cl. 75-78) ABSTRACT OF THE DISCLOSURE Copper is separated from lead by pouring molten lead bullion into the top of a column of molten bullion, progressively cooling the column downwardly to form zones, in the middle zone of which the Cu separates and rises to the top of the column where it is removed. The lead containing not more than 0.1% Cu is removed from the bottom of the column.

This application is a continuation of my copending application S.N. 576,344, filed Aug. 31, 1966, now abandoned, which in turn is a continuation-in-part of my then copending applications S.N. 372,576, filed June 4, 1964, now abandoned, and S.N. 537,159, filed Mar. 24, 1966, now abandoned, all for Method for Removal of Copper from Lead.

The extraction of metallic lead from lead ore in a lead blast furnace produces a lead bullion which, due to the reducing action, contains other alloying elements at the high temperature in the liquid lead. These elements are mainly the metals Cu, As, Sb, Sn, Bi, Ag, Au or their alloys with lead or other metals.

Because these elements in the proportion in which they are present in lead bullion unfavorably influences the chemical and mechanical properties of lead, the lead bullion must undergo a refining process. During the refining process of the lead bullion, the copper must first be removed and the removal must be as complete as possible. If this is not done, the copper accumulates in the various intermediate products of the refining and desilvering and makes the utilization of the intermediate products diflicult and expensive. The final decoppering of the lead bullion with sulphur to remove the copper as completely as possible is satisfactory, particularly if the copper contains tin. This is also one of the reasons why decoppering is always done before detinning, in other words, as the first step in any lead refining.

The decoppering of lead bullion generally takes place by separation or segregation processes because metallic copper and its compounds, as, for example, Cu S, Cu As and Cu Sb, are limitedly soluble in molten lead, and during solidification, they segregate completely or nearly quantitatively. This so-called decoppering of lead bullion takes place usually in two steps. In the first step, a farreaching segregation of copper or its compounds takes place with falling or rising temperature, that is to say, through slow cooling of the lead bullion close to the melting point of the lead-copper eutectic, which is practically identical with the melting point of lead, or through slow heating of the lead bullion up to a temperature just above the said eutectic temperature. By this process, a copper dross is segregated on the surface of the molten lead, first of a dough-like consistency which after stirring becomes dry and powdery. This dry condition indicates that the dross is separated from most of the mechanically adherent molten lead. Generally, the dry dross is removed with perforated ladles from the surface. This copper dross contains about to Cu, and As, Sb, Fe and S 3,392,011 Patented July 9, 1968 ice in small percentages onlysometimes less than 1%- and as a balance, lead. These elements are present as alloys with one another and combined with sulphur or oxygen. In the second step, the residual amount of copper, which may be 0.2% to 0.04% Cu, is removed with the addition of sulphur and by this means reduced to 0.1% to 0.002% Cu.

These known methods have the disadvantage that their performance requires considerably bulky apparatus as well as extensive manual work. This puts a heavy financial burden on the refinery. The copper dross so produced is of low value due to the low content of copper and the high percentage of other alloying metals which must undergo considerably costly metallurgical processing until the metallic copper is produced.

A method by which the first step of the decoppering of lead bullion is carried out continuously is also known. By this method, the lead bullion enters a reverbatory furnace which has a lead bath of 1.3 m. in depth. The temperature of the upper part of the lead bath is 800 C. to 900 C. and decreases towards the bottom of the bath to 400 C. to 500 C. Due to this temperature gradient, the copper segregates and, by the addition of sulphur bearing materials, is converted into a copper-lead matte. The lead content of this matte can be reduced by the addition of sodium sulphide. This copper matte has approximately 40% Cu and the decoppered lead has approximately 0.3% to 0.4% Cu. This method has the disadvantage that the copper content in the decoppered lead after the decoppering contains 0.3% to 0.4% copper and is therefore regarded as too high for further refining. Furthermore, in this method, an addition of sulphur-containing materials as well as sodium sulphide is necessary.

Williams, U.S. Patent No. 1,687,187, discloses a method by which copper can be separated from lead by forming a vertical column of molten bullion enriched with zinc, and cooling the column from a head temperature of about 600 C. to a bottom eutectic temperature of from about 315 to 330 C. Due to the decrease in the solubility of the lead, a mixture of lead and copper together with zinc, gold and silver separates out and rises to the top of the column in an enriched Parkes crust. The initial addition of zinc makes this a two-step process because the zinc must be removed in a further purifying step. The separated mixture contains at most from 30 to 40% copper because of the temperature gradient in the vertical column. Williams, in U.S. Patents Nos. 1,687,188 and 1,774,688, in order to obtain a greater yield of gold and silver, raises the temperature of the top of the column to not more than 850 C. He does not improve upon the purity of the copper content in the Parkes crust. In the Williams process, the separated lead is contaminated by the unseparated copper and other alloying metals.

This invention overcomes the stated disadvantages of the known methods, which means that the decoppering is carried out continuously in the first step and decoppered lead with 0.1% copper or less is producedJFurthermore,

the segregated copper phase has a considerably higher copper concentration compared with the previously known methods. The copper concentration is and more of metallic copper, particularly after removal of the mechanically adhering lead by hot pressing. This high copper concentration of the segregated copper phase naturally facilitates further treatment.

According to this invention, the lead to be decoppered flows into the upper part of a container. This container is filled with lead and the upper temperature is above 800 C. The temperature distribution in this lead column in the container is so adjusted that a temperature gradient with an upper temperature of at least preferably 950 C. is decreasing to an eutectic temperature of approximately 326 C. and down to 315 to 320 C. as the bottom temperature. The adjustment of the bottom temperature is achieved'by having on the bottom of the container a solidified crust of lead. Corresponding to this temperature gradient, the temperature of a vertical plane through the center of the lead column also decreases. In this way, the solubility of copper in lead decreases with decreasing temperature, and copper is segregated from the melt. A gravity segregation of copper to the surface of the lead column takes place when the solubility limit of copper in lead at the corresponding temperature is exceeded. The existing, or formed, copper compounds in lead are remelted and dissociated in the corresponding zones of the lead column in which the compounds reach their melting temperature. By this means, the copper of the dissociated compounds is gravity segregated and the residual part of the compounds is dissolved in the molten lead. At the bottom temperature of the column, the solubility of. all alloying elements in lead, with the exception of copper, is higher than their percentage in lead bullion and no segregation takes place. By this means, only the copper is accumulated on the surface of the molten lead column in the copper collector. The decoppered lead, which may contain 0.1% copper, leaves the container continuously through a central pipe, the opening of which is as close as possible to the solidified crust at the bottom to assure a temperature as low as possible. The amount of lead leaving the container is equivalent to the amount of the lead charged. By this means, the lead which is close to the solidification point is reheated in the central pipe and leaves the copper collector through a discharge pipe at a temperature of 100 C. to 200 C. below the temperature of the lead charged. At the same time, the descending lead stream is gradually cooled by the ascending lead stream in the central pipe by the principle of countercurrent flow. The solidified crust on the bottom assures a temperature as close as possible to the solidification temperature before the lead enters the ascending stream in the central pipe. During the working of the process, the solidified crust moves up and down, that is, it breathes. This solidification and remelting guarantees a constant bottom temperature which. corresponds to the actual eutectic temperature of the lead bullion. The distance between the solidified crust and the bottom opening of the central pipe should be as small as possible and is dependent on the heat extracted. This distance can be determined by a probe which passes' through the central pipe. The time the lead takes to pass through the container is dependent on the heat flow and is about 6 to 24 hours under industrial conditions. The heat equilibrium and the temperature gradient may adjust themselves or are adjusted by additional heating or cooling. By making the container barrel-shaped, it is possible to decrease the time required for the lead bullion to pass through the refining container.

In case of a container with a large diameter, multiple pipes for the ascending lead are provided. The metallic copper which accumulates on the surface of the lead column should preferably be protected from oxidation by an envelope of inert gas. The segregated copper phase is removed continuously or discontinuously.

The final decoppering takes place preferably with sulphur similar to present methods in use. The copper dross produced from this sulphur decoppering could be returned as charged into the lead blast furnace, thus differing from present methods, without additional cost to the refinery.

This invention reduces the copper content of the lead bullion to a residuary copper content of approximately 0.1% Cu or less by means of segregation of copper, and produces at the same time a solidified copper phase of approximately 80% Cu. Besides this, the invention allows the decoppering to be conducted continuously. The necessary apparatus is quite small, requires limited floor space in comparison to other methods, and also requires smaller capital outlay. Another advantage is the considerably lower operational cost. Further, the health hazard by lead poisoning is considerably reduced as compared with present methods.

In a modified form of this invention, the copper phase is also extracted in a molten state in a continuous segregation decoppering process and still keeps the composition of the decoppered lead at about 0.1% Cu or even less.

To this object, the upper part of the column is enveloped with a heating jacket and additional heat is supplied by, for example, combustion of gases inside the jacket, or by using the copper rich liquid phase inside the container as an electric resistance material thereby employing electric resistance heating. By this means, the temperature in the upper part of the lead column is increased to 1070 1250 C., preferably around 1100 1170 C.

The container is further provided with a discharge pipe at the level of the copper-rich phase. This pipe is also heated to prevent a solidification of the copper-rich molten phase. The discharge pipe is slightly bent to form a siphon and so prevent oxidation.

.The hot lead bullion is charged into a temperature zone preferably of approximately 850 to 950 C., in the upper part of the lead column. Beyond that zone, a zone of approximately 950990 C., which latter zone acts as a type of liquid membrane which allows the solid copper phase to pass upwards but at the same time restricts the liquid lead from doing so. Disturbance of this liquid membrane zone by the charged lead should be avoided.

Tapping of the liquid copper phase may be continuous or discontinuous, depending on the amount of copper phase accumulated. The tapped copper-rich phase is subjected, preferably after cooling, to generally kell-known mechanical pressure treatment whereby the adhering liquid lead is expelled and the copper content thus increased.

The means by which the objects of the invention are obtained are described more fully with reference to the accompanying drawings, in which:

FIGURE 1 is a vertical cross-sectional view through the apparatus used to perform the process of this invention; and

FIGURE 2 is a graph of the curves showing the copper separation obtained in examples of this invention.

As shown in FIGURE 1, refining container 1 is made of a seamless steel pipe 680 mm. high and 90 mm. in diameter with the bottom part closed by welding. The open upper end is closed by a hood 2. On the upper part of the refining container 1, a molten lead charge inlet 3 is situated. The central pipe 4 goes to the lead discharge outlet 5. Through an extension pipe 6 and the central pipe 4, a probe 7 is inserted. The hood 2 has an inlet 8 and an outlet 9 for the inert gas. Through the inlet pipe 8, 1 liter of nitrogen per hour is charged into the hood 2 which leaves the hood through the outlet pipe 9. The lead bullion to be decoppered is charged through the inlet 3 into the refining container 1 in an amount of 15 kg. per hour with a mean preheated temperature of 1050 C. This lead bullion as fed into the refining container contained 2.95% Cu, 0.3% As and 1.10% Sb. Because in this laboratory model the surface of the refining container in proportion to the volume of the lead column was considerably large, the heat loss was excessive. To overcome this laboratory difficulty, the refining container was heated by two independent electric resistance 'heaters. The temperature gradient was as follows, all heights being measured from the bottom: mm. height=340 C.; 220 mm. height=550 C.; 380 mm. height=885 C.; and 560 mm. height (above the lead discharge outlet 5)=920 C. The charge of lead entering the container through charge inlet 3 moves in a lead column 10 down to the bottom of the refining container 1 which had a solid lead crust 11. By this means, the lead cools according to the temperature gradient and the copper content is segregated and moves upwardly in the column. The decoppered lead then ascends through the central pipe 4 and is thereby reheated and leaves the refining container 1 through the lead outlet 5. In Example 1, the decoppered lead contains 0.11% Cu, 0.26% As, and 0.89% Sb. The segregated copper accumulates on the surface of the lead column in a copper Zone C is characterized by the gravity segregation and accumulation of metallic copper on top of the lead column. This Zone reaches from the melting point of the copper down to 900 C. The copper content rises steeply and the phase 12. After 20 hours and a total lead charge of 280 5 arsenic and antimony content rises only a little. kgs., the hood 2 was removed, 2.6 kg. of solid copper In larger refining containers and with larger amounts of phase was taken out, and under hot conditions, pressed to lead bullion passing through the containers, the accumulaa 1.1 kg. heavy copper cake which contained 88% metallic tion of the metallic copper in the copper-rich phase on copper and the balance, mainly lead. The balance of the the top of the lead column will be considerably higher than copper remained in the quenched lead column. This 10 on laboratory scale. By this means, only a light pressure column including the container was sliced by sawcuts for will be required to produce a metallic copper of 80% or the purpose of sampling. The time it took for a particle more from the copper-rich phase. of lead to pass through the container was 2 /2 hours. Only The copper-rich phase can also be removed in its molten seldomly did the solidified crust on the bottom remelt. t t F so d i th upper part f h container 1 i h the hme It took f the lead to P through the 1 provided with an eveloping heating jacket 13. Inside the wntamer h 2 hours as m Example the average space formed by jacket 13 and the container 1, combustible P CPntent m the decoppefed lead T 014%, and when gases are burned. At the level of the formed liquid copperthls tune was 3 g a q Exam? 6 then the average rich phase 12, a slightly bent discharge pipe 14 is posicopper comm? was tioned for removing the liquid copper.

The following table presents the distribution of the 50 Lead bullion was charged into the lead charge mlet 3 copper content in the lead column for the above laboratory of th Iefinino o 1 t th t f 15 k0 /h t experiments. The samples T1 to T8 for analysis were taken t e t i g g 1 1 from the fast-cooled lead column in different levels after P g ure 0 6 ea u Ion was 0 t e O completion of the experiment. The positions of the levels Owing composltlon from which the samples were taken are indicated by T1 Percent to T8 in the table, and the mean temperature in the ap- C11 2- propriate places of the three examples, a, b and c given S 0.27 in the table is shown by the curves a, b and c, respec- Sh 0.95 tively, in FIGURE 2. Sn 0.0005 Besides the alloying elements mentioned in the table, g 0.108 the following impurities in the lead were determined: 0.005 Zn=0.005%, Tl=0.0005%, Bi=0.0037%, Cd=0.0005%, 1 0.004 and Ni=0.00l%. Because the composition of these 21- C l 0.0005 loying elements did not change, they are not mentioned in N1 0.001 the table. and traces of Fe and T1.

TABLE Example Time to Pass Thru Container 2.5 Hours 2 Hours 3 Hours 011 Sb As Cu Sb As Sn Fe Ag Cu Sb As Analysis of Input 2.05 1.10 0.293 3.85 0.44 0.17 0. 0005 Pro. 0.108 2. 63 0. 50 0.020

Input Temperature 1,0501,150 C. l,050l,150 C. 1,050-1,150 O.

1.01 0. 20 0.85 0. 0.11 0. 0005 0.20 0.105 40.5 0. 0.10 0.80 0.00 15. 30 0.54 0. 05 0. 0005 0.14 0. 000 14.5 0.41 0.01 0. 35 0.00 2.55 0.24 0.005 0.0005 0. 40 0.115 3.2 0. 31 0.01 1.18 0.00 28.84 0. 00 0.22 0. 0005 0.12 0.088 31.0 1. 00 0. 001 1.00 1.20 27.52 0. 70 0.61 0. 0005 Trc. 0.003 24. 01 1.70 0.50 0.00 1.25 10.18 0. 57 0. 22 0. 0005 0. 22 0.108 12.01 1. 30 0.31 0. 00 0.78 N.d. N.d. N.d. N.d. N.d. N.d. 8.07 0.61 0.11 0.70 0. 30 0. 42 0. 34 0. 002 0.0005 0.13 0.121 0.40 0. 52 0.10 0. 0. 20 0.14 0. 51 0. 018 0.0005 0.110 0.10 0.48 0030 Stability of the Crust at the Bottom of Crust seldom rem ted Crust remelted often Crust was present during the the Container.

whole experiment In FIGURE 2, Zone A represents the zone in which the dross formation takes place. This zone covers the range from the solidification point up to a temperature of approximately 700 C. This is the zone in which the present elfective decoppering occurs. In this region, the copper is combined with arsenic and antimony and possibly other elements to form intermetallic copper compounds and copper cannot be recovered in the metallic form. The copper content rises to approximately 30% combined copper and at the same time, the percentage of antimony and arsenic rises due to the formation of intermetallics.

Zone B is the region of the dissociation of the dross compounds and reaches from approximately 650 C. to 900 C., and partly overlaps Zone A. In Zone B the copper is at a temperature at which it is insoluble and thus the intermetallic compounds of the copper are dissociated, and by this means, the metallic copper is gravity segregated in the lead column and the residue of the dissociated intermetallics is dissolved in lead. The copper, antimony and arsenic content decreases due to separation of the dissociated products in this region.

The bottom temperature of the container was kept at 315- 320 C. and the top temperature of the same at approximately 1170 C. The temperature of the discharged lead was approximately 1000 C., and the time needed for the lead to pass through the container was 2 hours.

The lead charged into the lead charge inlet 3 moved in a descending stream inside the lead column 10 towards the solid crust 11 at the bottom of the refining container 1. In this way, the lead cooled down and the copper content was segregated. The lead then rose in an ascending stream through the central pipe 4 and underwent reheating, leaving the refining container by the lead discharge pipe 5. The decoppered lead contained 0.11% Cu, 0.26% As, and 0.89% Sb.

Segregated copper accumulated on the surface of the lead column as a liquid molten copper phase 12.

After 20 hours and a lead charge of 280 kg., the lead discharge pipe 5 was closed and from the discharge pipe 14, 1.91 kg. of a liquid copper phase was extracted and cast into a conical brass mould. After cooling, the sample was cut into four sections and each was subjected to hot Cu ,.percent Pressed Cake I 89.2 Pressed Cake 11 I 8.2.4 Pressed Cake III- 81.3 Pressed Cake IV 79,8

Through the inlet 8 one liter of nitrogen-per hour was charged into the hood 2 and left the hood by the outlet 9.

A vacuum may be substituted in place'of the protective inert gasatmosphere which is particularly beneficial if degassing or the removal of volatile elements is advisable.

Having now described the means by which the objects of the invention are obtained, I claim:

1; A method for the continuous removal of copper and copper-rich phases from lead bullion by segregation in a vertical column of lead bullion formed by molten lead bullion, comprising forming a temperature 'gradientdecreasing from the top towards the bottom in the vertical lead column in which the upper zone has a temperature from about 1170'to 850C the intermediate zone 'a temperature from about 900 to 650 C., and the lower zone a temperature from about 750 to 315 C., forming a liquid membrane zone at the top of the column at a temperature of about 950 to 990 C., feeding the molten bullion to said column immediately below said membrane, separating the intermetallic copper compounds from the lead bullion in said lower zone, decomposing said copper compounds in said intermediate zone Whileleaving the other components dissolved in the lead, concentrating the insoluble metallic liquid copper at the top of said-"upper zone, passing said liquid copper upwardly through said liquid membrane which restricts the passage of liquid lead, removing the metallic copper from the top of the column, andremoving the lead containing not more than 0.1% copper from the bottom of said lower zone.

References Cited UNITED STATES PATENTS 1,535,743 4/1925 Stannard 75-78 1,687,187 10/1928 Williams.

1,687,188 10/1928 Williams 75-79 1,774,688 9/ 1930 Williams 75-79 2,109,144 2/1938 Betterton et al. 75-78 2,434,105 1/ 1948 Fleming et a1 7578 XR 3,317,311 5/1967 Davey 757-8 HYLAND BIZOT, Primary Examiner.

DAVID L. RECK, Examiner.

H. W. TARRING, Assistant Examiner. 

